Technical Field
The present invention relates to an atrial fibrillation detection system.
Background Art
Atrial fibrillation refers to a condition in which the atria twitch finely and cannot contract sufficiently, due to irregular and rapid stimulation throughout the atria. Meanwhile, since some stimulation of the atria travels through the atrioventricular node, the ventricles contract at irregular intervals, irrespective of the sinus rhythm. Thus, because the ventricles contract, albeit irregularly, and there is no marked loss of coronary function, many people fail to notice the symptoms of atrial fibrillation. It is estimated that there are about 1,000,000 patients suffering from atrial fibrillation within Japan, but it is thought that if people who fail to notice the symptoms were included, the number of patients would be far greater.
Since, the atria cannot contract sufficiently under atrial fibrillation, blood tends to pool within the atria, producing clots, leading to the possibility that such a clot may be transported to the brain, causing a cerebral infarction. Therefore, patients with atrial fibrillation are said to be about five times more likely to have a cerebral infarction than individuals without symptoms.
Because blood clots produced by atrial fibrillation are large in size, in many instances large blood vessels of the brain become obstructed. For this reason, a cerebral infarction that is caused by atrial fibrillation can inflict wide-ranging damage to the brain, making a prognosis that the individual will be left with an impediment severe enough to require nursing care highly likely. Nursing care may impose physical, psychological, and economic burdens on the family providing assistance, and is thought to impose a large economic burden on society as well.
While full recovery from atrial fibrillation may prove possible by reducing clot formation through the administration of drugs, or by catheter ablation, early detection is necessary to do so. However, as mentioned above, atrial fibrillation in many cases does not produce subjective symptoms. Moreover, in paroxysmal cases, the disorder may not be discovered by an EKG exam during a routine checkup or hospital visit.
Research has been carried out with the goal of using the heartbeat period to distinguish atrial fibrillation. For example, one such method involves calculating the distribution of the difference ΔR in adjacent heartbeat periods for a healthy individual and an atrial fibrillation patient, respectively, and automatically detecting atrial fibrillation by the Kolmogorov-Smirnov test. However, this method requires that heartbeat period values be taken over an extended period in order to obtain the ΔR distribution, imposing a burden on the test subjects. Moreover, it is possible that paroxysmal atrial fibrillation occurring within a brief time interval will not be detected.
Another method distinguishes atrial fibrillation based on a standard deviation obtained from a heartbeat period distribution (Patent Document 1). However, the technique disclosed in Patent Document 1 also requires heartbeat periods to be calculated, and therefore requires that heartbeat period values be taken over an extended period.
A further method distinguishes the condition through frequency analysis of heartbeat period fluctuations (Patent Document 2), but requires heartbeat period values measured continuously over several minutes for the purpose of frequency analysis, and it is possible that paroxysmal atrial fibrillation will not be detected.